Phase separation in wurtzite CuIn x Ga 1− x S 2 nanoparticles

It has earlier been reported that that the gallium incorporation in wurtzite CuInS 2 (CIS) results in structural distortion, non-homogeneous shape, and distribution of particles. However, a detailed study of the effect of Ga substitution on the structure and morphology has not been reported. Here, we report the synthesis of nanocrystalline CuIn x Ga 1− x S 2 ( x = 1, 0.7, 0.5, 0.3, and 0) wurtzite particles by solution processing in a nitrogen atmosphere. Structural analyses by X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the as-synthesized CuInS 2 (CIS) and CuGaS 2 (CGS) nanoparticle were single-phase wurtzite structures, whereas CuIn 0.7 Ga 0.3 S 2 , CuIn 0.5 Ga 0.5 S 2 , and CuIn 0.3 Ga 0.7 S 2 had three wurtzite phases having In-rich, In–Ga, and Ga-rich compositions. The shape of the resulting nanoparticles was either elongated, polygonal, or tadpole depending on the phase composition. In-rich particles had elongated rod-like morphology, the In–Ga particles were irregular hexagonal/equiaxed, while the Ga-rich phase formed with a tadpole morphology. The bandgap of the wurtzite-CuIn x Ga 1− x S 2 increased with Ga substitution: from 1.49 eV for CIS to 2.0 eV for CGS.